Conventionally, various sensors, such as gyro-type yaw rate sensors configured to resonate an oscillator and to detect movement of the oscillator, are employed for detecting a physical quantity.
Non-patent Document 1 discloses one example of a resonant circuit configured, as a yaw rate sensor, to send a detection signal of an oscillator to a drive circuit and to send an output signal of the drive circuit to the oscillator thereby to cause self-oscillation of the oscillator.
The drive circuit in Non-patent Document 1 includes a C/V conversion circuit, an AD converter, and a phase synchronization circuit. The C/V conversion circuit is configured to convert a capacitance signal (detection signal) received from the oscillator into an analog voltage signal. The AD converter is configured to convert the analog voltage signal received from the C/V conversion circuit into a digital signal. The phase synchronization circuit is configured to generate a synchronization signal based on the digital voltage signal received from the AD converter. Thus, the drive circuit receives, as a driving signal of the oscillator, the synchronization signal generated by the phase synchronization circuit and causes resonance of the oscillator.
[Non-Patent Document 1]
ISSCC2010, Digest of Technical Papers, pp. 6, 11 Feb. 2010
The configuration of Non-patent Document 1 requires the AD converter. It is noted that, in general, an AD converter is a relatively large and unreliable device and is apt to receive an effect of an environmental noise on its output signal. In consideration of these general factors about an AD converter, the resonant circuit as disclosed in Non-patent Document 1 and equipped with an AD converter may be hard to be downsized and may be insufficient in reliability and in tolerance for noise.